Running Ada 2012 On The Cortex-M4

Setup was easy since GPS was already installed. Setting up the ST-Link debug interface to the STM32 board (see the figure) actually took more time. It was then a matter of running through the flashing LED demo. I included a snippet of code from a flashing LED program to highlight some of the advantages of using Ada 2012 (see the listing).

with LEDs;      use LEDs; 
with Button;    use Button; 
with Ada.Real_Time; use Ada.Real_Time; 
package body Driver is 
   type Index is mod 4; 
   Pattern : constant array (Index) of User_LED := (Orange, Red, Blue, Green); 
   task body Controller is 
  Period     : constant Time_Span := Milliseconds (75);  -- arbitrary 
  Next_Start : Time := Clock; 
  Next_LED   : Index := 0; 
   begin 
  loop 
     Off (Pattern (Next_LED)); 
     Next_LED := Next_LED +  
       (if Button.Current_Direction = Counterclockwise then -1 else 1); 
     On (Pattern (Next_LED)); 
     Next_Start := Next_Start + Period; 
     delay until Next_Start; 
  end loop; 
   end Controller; 
end Driver;

Even if you haven’t used Ada, you should be able to get an idea of what’s going on. In particular, the task body definition highlights the built-in multitasking support. Also note the use of the “modular” (unsigned) data type for Index that limits the addressing of the Pattern array. Unlike C, there is no need to check the result of Next_LED when it is updated. Additionally, I prefer the more verbose if/then/else conditional expression of Ada to the C/C++ ?: combination. I have programmed in APL, and its one-liners were neat but typically indecipherable. C and C++ code can get this way too.

Ada has a number of benefits compared to C and C++ (see “Ada Offers Advantages Over C And C++” on electronicdesign.com). But it has drawbacks as well, such as availability. For ARM Cortex microcontrollers, this is no longer an issue. Developers can take advantage of all the Ada 2012 features, from generics to multitasking.

I would encourage anyone wanting to write bulletproof code for embedded applications to check out the AdaCore/STM32 combination. It is inexpensive and very functional. The ST-Link support also allows it to work with platforms like the STM32F401 Nucleo (see “Extensible Prototyping Board Built For STM32 MCUs” on electronicdesign.com). I tried it on my Nucleo as well.

The Heartbleed bug (see “What Heartbleed Should Teach Embedded Programmers” on electronicdesign.com) is just one of many reminders of how one range check error can wreak havoc. C does not do it, but Ada does check—and not just on array access, by default. Ada will not eliminate all bugs from your code, but it does make it a lot harder to create them.

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